1. Field of the Inventions
The present inventions relate to an outboard motor mounted to the outside of a hull, and more particularly to an outboard motor designed to reduce the amount of water entering a cowling and becoming trapped in a bottom part of an engine compartment, as well as arrangements for discharging water or seawater that entered the cowling.
2. Description of the Related Art
Conventionally, outboard motors include an engine inside of a cowling. An intake air duct is usually designed to guide air through the cowling and toward the engine, and such ducts often have a water-separating structure for reducing the amount of water entering the cowling. The intake air duct should have a cross sectional area sufficiently large to provide an adequate amount of air for the engine to operate within its design parameters. Thus, it can be difficult to keep all water out of the intake air duct. Such water can run on the top face of a flywheel magneto cover, for instance, and can remain at a bottom part of the engine compartment within the outboard motor.
Further, such water trapped in the bottom portion of the cowling might be splashed onto the engine and accessory equipment due to vibration or change in the attitude of the outboard motor, resulting in corrosion. Also, the water might be sucked into an intake pipe into the engine.
Salt in seawater can stick to various components of the outboard motor, which can damage its outer appearance. In addition, when a seal for sealing the top cowling to the bottom cowling deteriorates, water might enter the cowling enclosure through deteriorated portion and be trapped in the bottom part, resulting in the foregoing problems.
In order to reduce the amount of water entering the cowling enclosure of outboard motors, some outboard motor cowlings include what is referred to as a “duckbill-type” check valve.
For example, FIG. 11 illustrates a known duckbill-type check valve 100 designed to drain water under the weight of the water itself applied to the valve 100. As such, it takes time for water that entered a cowling 101 to be drained through the valve 100. Further, when the engine 110 operates, it draws in intake air 200 from the interior space within the cowling 101. Thus, a negative pressure is produced in the cowling 101 which interferes with the operation of the duckbill-type check valve 100, preventing water from being drained. As a result, it takes more time for the water trapped in a bottom part 102 to be completely drained, raising the likelihood that the water will be splashed in the bottom part 102.
Other outboard motors include, with reference to FIG. 12, an extended duckbill-type check valve 100. This “extended” type of duckbill check valve 100 generates a head difference D1 between a drain hole 100a of the duckbill-type check valve 100 and the bottom part 102, where water is trapped. This design reduces the effect of the negative pressure produced by the flow of intake air 200 into the engine 110 so that the water trapped can be drained more quickly. With this design, water can be drained without being affected by a negative pressure produced with the operation of the engine 110 as long as the head difference D1 is a predetermined value or larger when the negative pressure is a predetermined value or smaller.
With reference to FIG. 13, where extended duckbill valves are used, there is a limit to the magnitude of the head difference D1 that can be generated due to the limited space available within the cowling 101. Thus, in the case in which a higher negative pressure is produced by the flow of the intake air 200 with the operation of a larger outboard engine, for example, the head difference D1 required to compensate for the effect of the negative pressure cannot be provided, so that water 120 may not drain sufficiently quickly.
Further, as noted above, the duckbill-type check valve 100 is designed to drain water under the weight of the water itself. Thus, with reference to FIG. 14, when the outboard motor encounters a big wave 201 in rough weather, or during deceleration or reverse operation of the watercraft, for example, and a large volume of water 120 enters the cowling 101 all at once, the water 120 can be trapped in the bottom part 102. Further, as shown in FIG. 15, the conventional duckbill-type check valve 100 cannot function normally when the outboard motor encounters a big wave 201 and is soaked in the wave up to an upper part of the outboard motor, or up to a position above the duckbill-type check valve 100.